Although periodic amplitude modulation of echoes from birds were observed in the very first recordings of birds with radar, few publications on the topic are found in the literature. The phenomenon, which tends to be correlated with the wing beat frequency (WBF), has been suggested as a feature for discrimination between bird species. Early studies were reported mainly in the 1960s and 1970s, however, several questions remain unanswered. Is such modulation prevalent, if so what causes it, how does it vary with aspect angle and signal to noise ratio (SNR), how sensitive is it choice of carrier frequency, and what is its potential as a feature for classification in a real scenario? This paper seeks to address several of these question. The discussion and results presented are based on analysis of X-band radar data and video of flying gannets. These measurements are supported with electromagnetic predictions of 3D gannet models.
Known as a useful tool to simulate SAR image, the MOCEM software has been recently extended. Now, its version 4 includes new features to simulate the radar raw data of a maritime scene composed of a ship on a dynamic sea surface. This paper describes the latest developments of the software and illustrates the work done in the context of a cooperation involving FFI (Norway) and DGA MI (France). Thanks to work done by Alyotech, MOCEM now benefits from GPU computation. This offers to take into account the ship motion in the computation of the raw data for SAR and ISAR simulations. It offers to display, in real time, the phenomena of delocalization, defocusing and deformations encountered in images when dealing with complex and realistic ship motion. In the first phase of the cooperation FFI and DGA MI have produced a methodology of how to build a 3D EM model of ships using rough CAD models (bought from internet provider). Some works have been done to adapt them to an EM application and to allocate EM properties. In a second step, simulations have been done to produce raw data to be been processed with SAR/ISAR algorithms. In parallel, real acquisitions have been done by FFI using the PicoSAR radar (bought from SELEX). In the end, simulations and measurements have been compared in order to demonstrate that simulation has reached a high level. Therefore, simulation of a new radar equipment has become a real option to optimize processing, reduce flight tests or for the training of future users, such as radar operators of a maritime patrol aircraft.
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